Field of the Invention
The present invention pertains to the field of satellite navigation technology, and more particularly to a method for assessing a quality of a radio frequency (RF) signals for a satellite navigation system.
Description of the Related Art
In a navigation system, satellite navigation signals are used for timing and ranging. This is reflected in three aspects related to navigation performance carrier tracking performance, pseudo-code tracking performance, and message demodulation performance Navigation signal framework determines the inherent performance of a navigation system, while spatial signal quality determines the difference between the best achievable performance of an actual navigation system and the performance of the signal framework. The design of a communication system is aimed at correct demodulation of information, and the performance of a communication system is in relation to error of a sampling decision moment signal vector; whereas the design of a navigation system is aimed at ranging accuracy, which depends on quality of signal waveform. Therefore, a navigation system requires higher signal quality than a general communication system, and accordingly, it puts forward higher requirements in comprehensiveness and accuracy to signal quality assessment methods thereof.
The prior art has proposed a number of quality assessment schemes for satellite navigation systems. For example, CN102571652A discloses a method for assessment of GNSS baseband signal, in which GNSS baseband signal performance is analyzed in aspects of frequency-domain power spectrum, time-domain waveform, code-chip edge, modulation error as well as some related characteristics. However, further studies show that the above schemes still suffer from the following limitations:                1) The method only takes into account assessment of baseband signal quality, thus cannot truly reflect the impact of spatial signal quality to navigation performance, and it does not include a signal processing method for non-distortion frequency conversion from radio frequency signal to baseband; moreover, because the method employs a baseband sampling mode, it requires different analog channels to be configured for signals at different frequency points, which inevitably introduces time-delay inconsistency among these analog channels, resulting in decreased accuracy of the assessment of inter-frequency signal consistency;        2) The six assessment metrics of an eye diagram are somewhat idealized, and difficult to be applied in quality assessment of a composite signal containing three or more branch signal components in current GNSS, while such composite signal is a main form of signals adopted in currently mainstream four major navigation systems, namely, BeiDou, GPS, Galileo and GLONASS;        3) The method for assessment of quadrature phase error and magnitude imbalance has a narrow applicable scope, generally being used for QPSK modulation, and is also difficult to be applied in quality assessment of a composite signal containing three or more branch signal components in current GNSS; and        4) The method does not explicitly explain the relationships between these metrics and signal-acquisition, signal-tracking and signal-demodulation, thus it cannot result in a quantitative assessment of the impact of signal quality to navigation performance        